Technical Field
The present invention generally relates to low resistance source/drain contacts in complementary metal oxide semiconductor (CMOS) devices, and more particularly to devices and methods for making the same.
Description of the Related Art
In nanometer scale devices, conventional metal liner contact schemes are generally limited by high contact resistivity, especially in n-type field effect transistor (NFET) regions and p-type field effect transistor (PFET) regions. In some conventional contact schemes, for example, contact resistivity for either the NFET or PFET region is above 3×10−9 ohm·cm2, and more typically approximately 5×10−9 ohm·cm2. Accordingly, high contact resistivity increasingly impacts device performance.
In complementary metal-oxide-semiconductor (CMOS) technology, conventional processes result in one side (e.g., the NFET region or PFET region) of the device having a contact resistivity of approximately 5×10−9 ohm·cm2 while the other side has a contact resistivity of approximately 4×10−9 ohm·cm2. Source/Drain implantation process can be limited by short channel concerns that impact the transistor gate control and inability of sustaining homogeneity of high concentration of dopants through subsequent high-temperature thermal steps. For example, some implanted light atoms, such as Boron, scatter into the channel region resulting in high Drain-Induced-Barrier-Lowering (DIBL) effect and high off current. Some source/drain implantation processes are also limited by low dopant activation, as certain implanted elements have low solubility in the source/drain semiconducting material. The chemical doping concentration may be high exceeding chemical solubility limits in the source/drain material, but excess implanted dopants are not activated, but rather segregate into stable clusters or precipitates. Further, integration of trench epitaxy (EPI) contacts is complicated and challenging due to separate growth of n-type and p-type epitaxy materials in Middle-Of-Line (MOL) post source/drain and gate formation. In addition, separate patterning of the n/p doped regions for n-type and p-type epitaxy materials in MOL formation can cause yield loss.